Marking of materials is an important feature for identifying the origin of the articles. Traditionally, such marking is accomplished through the packaging of the materials, on which packaging information can be supplied on the producer, content and other features of the packaged materials. However, once the articles are unpacked, said information is lost. This is especially cumbersome if the user of the articles later has a need to identify the origin of the material. Such a need can occur when the articles are malfunctioning. Another use of marking is to prove fraud or forgery. Examples of articles for which marking would be advantageous are clothing, shoes, cigarettes, watches, bank notes, paints, explosives, pharmaceutical products, food products, cosmetic products, animals and agricultural products such as (pot)plants, cuttings, tissue culture materials and seeds.
In the prior art several systems using microparticles for marking materials have been described. Most of these systems use coloured or otherwise labelled microparticles which can provide a code, either by the manner of deposition of the microparticles on the material (thus offering systems which function like a bar-code) or by the intrinsic properties of the microparticles themselves. Examples of such systems are described in (amongst others) U.S. Pat. No. 3,772,099 (luminescent microparticles from a lanthanide and potassium silicate), U.S. Pat. No. 4,390,452 (microparticles forming coloured layers), WO 2003/052025 (microparticles of YVO4 or LaPO4 doped with euridium or cerium), WO 2002/46528 (fluorescent microparticles for forming patterns), U.S. Pat. No. 6,620,360 (multilayers of microparticles) and U.S. Pat. No. 6,455,157 (“bar-coding” with microparticles). In WO 2005/118650 a system is described in which polymer microparticles are doped with a dye, a rare earth element or with radioactivity for marking materials.
WO-A-90/14441 describes a method for tagging a material by treating the material with a nucleic acid taggant so that the nucleic acid attaches to said material in an amount sufficient for subsequent detection. For detection the taggant may be recovered from the tagged material.
Marking of materials is especially important in agriculture in the case of seeds. Once the seeds have been sown, it is practically impossible for a seed supplier to identify if a seed originates from the supplier's company. In this case, the microparticles of the prior art as discussed above are not or less useful, since they are toxic for the seed or the developing seedling, and/or they are dissolved in the earth in which the seeds are sown, and/or they are easy to copy, and/or are already in use for other purposes, other seed lots, other companies etc and therefore are not discriminative.
Thus there is still need for alternative marking microparticles, especially for the marking of seeds.